It hardly needs to be said that the chassis is a crucial component of a vehicle. It is the core of the vehicle, from which all other components are supported either directly or indirectly. It is ultimately responsible for absorbing and transmitting the forces experienced by the vehicle; its rigidity determines (to a large extent) the handling behaviour of the vehicle and its deformation behaviour is a major factor in the crashworthiness of the vehicle.
It is also the largest single component of the vehicle and (aside from the engine, in some cases) the heaviest. This means that the resources needed to construct the chassis and its eventual weight will be a significant part of the lifecycle environmental footprint of the vehicle.
Reduction of the weight and material requirements of the chassis will therefore lead to benefits in the performance, fuel economy and environmental footprint of the vehicle. However, this must be done without adversely affecting the necessary rigidity of the chassis.
Historically, a simple ladder chassis was constructed, using two longitudinal sections joined by crossmembers that (in effect) provided the “rungs” of the ladder. The longitudinal sections needed to be of a very large gauge in order to provide the necessary strength. This resulted in a chassis that, by today's standards, is too heavy and insufficiently rigid in torsion. It was, however, very straightforward to mass-produce.
The use of additional longitudinal sections joined by multiple crossmembers or bulkheads creates what is usually referred to as a tubular frame chassis. For mass-produced vehicles, these have however been dismissed as the time required for manufacture is generally too great.
Whilst the rigidity of such a structure is greater than that of a ladder chassis, in order to provide sufficient rigidity it is generally necessary to add additional diagonal members to the structure so that torsional moments are avoided and all forces are taken up by way of longitudinal tension or compression of a frame member. A structure of this type is usually referred to as a space frame, and is far too complex for mass production.
Modern volume-produced vehicles therefore universally use a pressed steel chassis. The chassis is formed by a pressing/stamping operation involving one or more steps. This produces a steel chassis which has the necessary rigidity but which is very heavy and requires very substantial tooling for its production. The remaining necessary parts of the vehicle structure are then spot-welded to the assembly.
The tools required to form the chassis are physically large, and must therefore be housed in a large facility. A substantial material cost (with attendant environmental footprint) is therefore involved in the chassis, the tools and the facility, the weight of the resulting chassis imposes a substantial ongoing environmental footprint as a result of the consequential energy requirements of the vehicle, and the large facility imposes a corresponding ongoing environmental footprint in terms of its heating, its lighting, its maintenance and so on. The necessary spot-welding involves significant energy consumption.
Our application WO2009/122178 described a chassis based on a steel framework complemented by a sheet or sheets bonded thereto. That application suggested the use of composite sheets. The content of that application is hereby incorporated by reference, and the attention of the skilled reader is specifically directed to that application for a fuller understanding of the present invention.